A non-contact method for spatially localized sedimentation of particles from liquid suspensions using Marangoni forces

This paper presents the directed sedimentation of suspension particles in a thin layer of liquid ( 1 mm) onto a featureless glass substrate by Marangoni flows. A programmable 16 × 8 array of surface mount resistors suspended 0.1–2 mm above the liquid provides dynamic millimeter-sized heat sources to locally heat the liquid surface to temperatures from approximately 28.5 to 36.5 ◦C. The heaters in this array can be activated independently by a graphical user interface, creating surface tension gradients along the liquid surface. The resulting Marangoni flows direct spatially localized particle sedimentation on the substrate. The resultant sedimentation patterns and accumulation levels depend on factors such as the temperature gradient at the liquid surface, number of active heaters and type of liquid used. For example, when a single heater is activated, a liquid surface temperature elevation of 6.9 ◦C results in a localized sedimentation of suspended weed pollen Kochia scoparia ( = 25 μm) in silicone oil DC-704 over a region of 2.9 mm2 that is centered directly beneath the active heater. This sedimentation method is a contactless technique, which reduces the likelihood of sample contamination. (Some figures in this article are in colour only in the electronic version)